A disk cartridge is disclosed in the Japanese Patent Application Laid Open No. 2003-109343. In the disk cartridge, a write/read opening formed in a cartridge body is closed by a pair of shutter plates coupled with each other. In this disk cartridge, if the pair of shutter plates closing the opening in the cartridge body is forcibly pushed, for example, a clearance will arise between the shutter plates and the perimeter of a first opening in the cartridge body. Dust or the like will possibly enter the cartridge body through the clearance. The dust or the like adhering to a disk encased in the cartridge body will make impossible correct write or read of information signals to or from the disk.
To design a smaller disk cartridge which houses an optical disk having a smaller diameter and which adopts the same recording format as that in the disk encased in the above disk cartridge, it is not sufficient to reduce only the dimensions thereof because, for maintaining the compatibility of a disk recorder and/or player with various disk cartridges different in size from one another, the write/read opening, in which an optical pickup comes when a disk cartridge is loaded into the disk recorder and/or player, may not be reduced in dimensions but should have the same size as that of a write/read opening through which write and/or read is made to and/or from a disk cartridge having the dimensions. Therefore, the write/read opening will take a large part of the entire size of such a small disk cartridge and thus the disk cartridge itself will have any lower rigidity.
If the cartridge body is more easily flexible because of the lower rigidity, for example, a clearance is more likely to arise between the shutter member and cartridge body and dust or the like will easily come into the cartridge body. Also, the cartridge body and shutter member will possibly be flexibly deformed and touch a disk in the cartridge body. If the disk is damaged by the dust or the like adhering to the disk and by the cartridge body or shutter member touching the disk, no correct write or read information signals to or from the disk will be possible.